1. Field of Invention
This invention relates to the switching of multiple access and/or multiplexed signals and more particularly to the switching of multiple access and/or multiplexed spread spectrum signals. More specifically, this invention relates to the switching of multiple access spread spectrum signals at a beam level, such as in a satellite system where an origination signal contains information from a plurality of users that is destined to a plurality of users which are located on separate destination beams.
2. Description of Related Art
Traditionally, satellite communication systems consist of a “bent-pipe” arrangement in which signals originating from a ground station have to be transmitted to a ground-based switching center where the switched signal is transmitted back to the satellite. This added transmission hop introduces additional delay and, in the case of cellular/PCS type communication, the delay is both noticeable and intolerable.
It is conventionally known to use a repeater located on the satellite to retransmit a signal from one ground station to another ground station. See, for example, U.S. Pat. Nos. 4,901,307 and 5,103,459, both to Gilhousen et al. Such conventional bent pipe systems simply repeat the origination beam on a particular destination beam without decoding and recombining multiple individual signals onto multiple destination beams.
It is also conventionally known to control contention for spread spectrum satellite communications using retransmission schemes for lost or corrupted code division multiple access (CDMA) originating signals. See, for example, U.S. Pat. No. 5,084,900 to Taylor. CDMA is a multiple access scheme using code sequences for identifying traffic channels in a common radio channel.
Various techniques are known for on-board satellite controller and switching matrices. See, for example, U.S. Pat. No. 4,926,422 to Alaria et al. However, in such conventional spread spectrum satellite communications systems and methods, a satellite receives a CDMA origination signal originating from a user and then repeats the user's signal on the appropriate destination beam.
In some conventional satellite communications systems, such as particular ground station spread spectrum encoders, CDMA signals incoming to a particular base station are encoded into a combined origination signal and transmitted to a satellite. See, for example, U.S. Pat. No. 5,757,767 to Zehavi. Such conventional spread spectrum satellite communications systems receive a multiple user CDMA origination signal and decode the user signals at the satellite. Subsequently, the user signals are recombined according to the destination beams.
Alternatively, methods are known in which multiple user signals are encoded at a base station into a single CDMA origination signal. See, for example, U.S. Pat. No. 5,805,579 to Erving et al., U.S. Pat. No. 5,566,164 to Ohlson and U.S. Pat. No. 5,764,630 to Natali et al.
Methods are also known for encoding a signal at the transmitting customer premises equipment (CPE) to ensure end-to-end integrity during travel to the encoded signal destination. See, for example, U.S. Pat. No. 4,577,313 to Sy. Such encoding of the signal at the transmitting CPE ensures data integrity through to a destination by preventing the signal from being decoded and recombined.
More complex on-board switching designs require digital hardware elements for each user signal, e.g., call, which greatly increases installation and maintenance costs, user service rates, and decreases signal-to-interference (S/I) ratios. Alternatively, it is conventionally known to minimize active on-board satellite switching in a satellite communication system. See, for example, U.S. Pat. No. 4,813,036 to Whitehead. Origination signals from ground stations to the satellite are transmitted on predetermined carrier frequencies that are dedicated to particular satellite destination beams. This results in the signals being repeated with no need for on-board switching.
Additionally, U.S. Pat. No. 5,805,579 to Erving et al. discloses an on-board switching system that processes origination beams and the included traffic channels at a symbol level rather than at the bit level. However, the symbol level corresponds to the user level. While the system has reduced complexity when compared to a switching system that switches signals at the bit level, the system is still very complex since there must be circuitry to determine the destination of each user signal. Accordingly, only when the destination of each user signal has been determined, can the signal be switched to the appropriate destination beam.